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Changes in Climatic Water Balance Drive Downhill Shifts in Plant Species’ Optimum Elevations
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Uphill shifts of species’ distributions in response to historical warming are well documented, which leads
to widespread expectations of continued uphill shifts under future warming. Conversely, downhill shifts
are often considered anomalous and unrelated to climate change. By comparing the altitudinal
distributions of 64 plant species between the 1930s and the present day within California, we show that
climate changes have resulted in a significant downward shift in species’ optimum elevations. This
downhill shift is counter to what would be expected given 20th-century warming but is readily
explained by species’ niche tracking of regional changes in climatic water balance rather than
temperature. Similar downhill shifts can be expected to occur where future climate change scenarios
project increases in water availability that outpace evaporative demand.
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The Greening of Synfuels
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An old, dirty technology to make transportation fuels from coal could
fight global warming, say proponents. The trick is using more biomass
and burying the carbon dioxide that’s generated
18 APRIL 2008 VOL 320 SCIENCE
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All Downhill From Here?
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Biologists say climate change may already be affecting high-mountain ecosystems around the world, where plants and animals adapted to cold, barren conditions now face higher temperatures and a surge of predators and competitors
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Human Evolution Out of Africa: The Role of Refugia and Climate Change
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Although an African origin of the modern human species is generally accepted, the evolutionary
processes involved in the speciation, geographical spread, and eventual extinction of archaic
humans outside of Africa are much debated. An additional complexity has been the recent evidence
of limited interbreeding between modern humans and the Neandertals and Denisovans. Modern
human migrations and interactions began during the buildup to the Last Glacial Maximum,
starting about 100,000 years ago. By examining the history of other organisms through glacial
cycles, valuable models for evolutionary biogeography can be formulated. According to one
such model, the adoption of a new refugium by a subgroup of a species may lead to important
evolutionary changes.
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Rescuing Wolves from Politics: Wildlife as a Public Trust Resource
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Long-term conservation of gray wolves is
possible if states recognize a legal obligation
to conserve species as a public trust resource
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Rapid Range Shifts of Species Associated with High Levels of Climate Warming
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The distributions of many terrestrial organisms are currently shifting in latitude or elevation in responseto changing climate. Using a meta-analysis, we estimated that the distributions of species haverecently shifted to higher elevations at a median rate of 11.0 meters per decade, and to higher latitudes
at a median rate of 16.9 kilometers per decade. These rates are approximately two and three times faster than previously reported. The distances moved by species are greatest in studies showing thehighest levels of warming, with average latitudinal shifts being generally sufficient to track temperature
changes. However, individual species vary greatly in their rates of change, suggesting that the range shift of each species depends on multiple internal species traits and external drivers of change. Rapid average shifts derive from a wide diversity of responses by individual species.
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Seeds of Change for Restoration Ecology
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FORESTS PROVIDE A WIDE VARIETY OF ECOSYSTEM SERVICES, INCLUDING PROVISIONS SUCH AS
food and fuel and services that affect climate and water quality (1). In light of the increasing
global population pressure, we must not only conserve, but also restore forests to meet the
increasing demands for ecosystem services and goods
that they provide (2). Ecological restoration has recently
adopted insights from the biodiversity-ecosystem function
(BEF) perspective (3). This emphasis on functional
rather than taxonomic diversity (3, 4), combined with
increasing acceptance of perennial, global-scale effects
on the environment (5, 6) and the associated species
gains and losses (“Terrestrial ecosystem responses to
species gains and losses,” D. A. Wardle et al., Review,
10 June, p. 1273), may be the beginning of a paradigm
shift in forest conservation and restoration ecology. As
a result, we may see increased tolerance toward and the
use of nonnative tree species in forests worldwide
8 JULY 2011 VOL 333 SCIENCE
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From Ocean to Stratosphere
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Rising tropical sea surface temperatures
alter atmospheric dynamics at heights of 16 kilometers or more.
SCIENCE VOL 322 3 OCTOBER 2008
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Linked in: Connectiong Riparian areas to support Forest Biodiversity
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Many forest-dwelling species rely on both
terrestrial and aquatic habitat for their
survival. These species, including rare and
little-understood amphibians and arthropods,
live in and around headwater streams and
disperse overland to neighboring headwater
streams. Forest management policies that
rely on riparian buffer strips and structurebased
management—practices meant to
preserve habitat—address only some of
these habitat needs. They generally do not
consider the overland connectivity necessary
for these species to successfully move across
a landscape to maintain genetically diverse
populations.
Management in headwater areas also can
affect downstream salmon habitat. Landslides
and debris flows initiated in these areas can
severely degrade habitat by dumping too
much sediment and not enough large wood
into the stream. Carefully managing sensitive
headwater areas can aid not only amphibians
and arthropods, but also threatened salmon
populations and other forest organisms.
Pacific Northwest Research Station scientists
are exploring scenarios for protecting
headwaters by extending riparian buffers
and connecting them over ridgelines to
neighboring drainages. A range of management
practices designed to achieve multiple
objectives may be appropriate in these
protected areas to facilitate cost-effective,
ecologically integrated management plans.
Headwater links could piggyback on lands
that are already protected and could consider
such factors as sensitivity to debris flows and
landslides, land ownerships and objectives,
and climate change.
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Mount St. Helens: Still Erupting Lessons 31 Years Later
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The massive volcanic eruption of
Mount St. Helens 31 years ago provided
the perfect backdrop for studying the
earliest stages of forest development.
Immediately after the eruption, some
areas of the blast area were devoid
of life. On other parts of the volcanic
landscape, many species survived,
although their numbers were greatly
reduced. Reassembly began at many
different starting points along the
spectrum of disturbance. Within the
national volcanic monument, natural
regeneration generally has been
allowed to proceed at its own pace.
Charlie Crisafulli and Fred Swanson,
scientists with the Pacific Northwest
Research Station, along with numerous
collaborators, have found that the sunlit
environment, dominated by shrubs,
herbs, and grasses that characterize
early-seral ecosystems, supports complex
food webs involving numerous
herbivores. These biologically rich
areas provide habitat for plant and
animal species that are either found
only in these early-seral ecosystems or
reach their highest densities there.
Although much of the focus of forest
ecosystem management over the past
20 years in the Pacific Northwest has
been on protecting old forests and
hastening development of conditions
associated with older forests, the
research on Mount St. Helens points
to the ecological value of allowing a
portion of a managed landscape to
develop characteristics of a complex
early-seral ecosystem
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